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To test the charging system,
connect a voltmeter set higher than 12v
as shown above with the engine running.
If the charging system components are
operating normally, the reading should be
between 13.5v and 14..4 volts. At rest
with the engine off, a fully charged
battery will read about 12.5v.
A word of caution: NEVER remove a battery
cable from the battery while the engine
is running to check to see if the
alternator is working or for any other
reason. This is extremely hard if not
fatal to an alternator and possibly the
regulator. The alternator has diodes
inside that may be damaged when the
battery cable is removed or replaced
while the engine is running. If the
charging system is working properly, this
test will show the 13.5v to 14.4v and you
will know the alternator is charging. |
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If your battery keeps draining
after sitting for a short time, you may
have a parasitic drain from the
electrical system. To check for a power
drain, connect a voltmeter as shown with
the ignition off and all components
turned off. If there is current then
something is draining the battery. The
ideal voltage reading for a classic
Mustang at rest is 0 to 1.5 volts.
Sometimes when you are trying to get a
reading for a drain, you might see a
slight reading at first. If everything on
the system is turned off, then there is a
residual current that needs to be drained
off. Just open the doors to "turn
on" the courtesy lights and then
close them. You should then be ready to
start your checks. To attempt to locate
the drain, perform the following:
1. Remove the fuses from the fuse panel
behind the dash and then check your
voltage reading. If your drain is gone,
then one of the fused circuits of the
system is causing the drain. Reinstall
the fuses one by one and check the
voltage reading with each fuse. When the
drain returns with a reinstalled fuse,
that is the circuit that is at fault.
Using a wiring diagram, trace the
components on that circuit to find the
cause. Unplug each component of the
circuit separately and check your
voltage. The faulty component will stop
the drain when it's unplugged.
2. If the drain still remains after all
of the fuses are removed, then the fault
is in a main component such as the
alternator, voltage regulator, starter
solenoid, or even the starter. One by one
unplug these components. When the faulty
component is unplugged, the drain will
stop and you will have found the cause of
the drain. |
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| Things to remember: |
1. The older Mustangs did not have any components
that constantly pulled current from the battery.
One problem that can arise is if your Mustang is
equipped with a factory clock. The clocks ran on
a points and spring mechanism. A spring loaded
gear would tick down the seconds until a set of
points closed thus making contact and receiving a
current signal from the battery. At that instant
the points repel each other, the gear spins
around winding the spring, and the seconds count
down again. If the points are bad, they can touch
and not make good contact to repel each other but
still pull current from the battery. This has
been a puzzler for a lot of people over the
years. If the clock is causing a drain,
unplugging it will stop the drain and you will
know it's the culprit.
2. Don't assume any component or switch is immune
to causing a power drain. In one instance, I had
a stoplight switch that was shorting against the
brake pedal. When I removed the switch and
checked it, it checked out fine. I reinstalled it
and the drain returned. I replaced it with a new
one and the drain disappeared. |
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| Jumping
A Low Or Dead Battery |
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When jumping your Mustang from
another vehicle, connect the jumper
cables as shown above.
Always connect the positive leads first
and remove them last. |
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